1. Field of the Invention
The present invention relates to an objective lens actuator that is provided to an optical pickup device for projecting a light beam to an optical recording medium so that record of information or reading of information can be performed. In particular, the present invention relates to a structure of the objective lens actuator in which an objective lens holder is held by a rod-like elastic member. The present invention relates also to an optical pickup device equipped with the above described objective lens actuator.
2. Description of Related Art
Recently optical recording media including a compact disc (hereinafter referred to as a CD) and a digital versatile disc (hereinafter referred to as a DVD) are widely spread. When information is recorded on or reproduced from such an optical recording medium, an optical pickup device is used, which projects a light beam to the optical recording medium so that information can be recorded or read. In such an optical pickup device, it is required that a light beam emitted from a light source is condensed with high accuracy on a recording surface of the optical recording medium through an objective lens. As a structure to realize the above described requirement, the objective lens actuator becomes indispensable.
As for the objective lens actuator, there is a type of the objective lens actuator which is provided with an objective lens holder holding the objective lens, is held by a plurality of metal wires having elasticity in a shakable manner with respect to a base member. Such an objective lens actuator is provided generally with a focus coil and a tracking coil on the objective lens holder, and with a permanent magnet on the base member. A base plate is stood on the base member and one end of each of the above described metal wires is connected to the base plate, and at the same time, other end of each of the metal wires is connected to the focus coil, the tracking coil and the like. Further, each of the metal wires is adhered to the objective lens holder with an adhesive agent, a solder or the like.
In the objective lens actuator as described above, electric current is supplied to the focus coil, the tracking coil and the like through each of the metal wires. By this arrangement, the objective lens holder is driven in its micro motion by an electromagnetic action with the permanent magnet to perform a focus adjustment, a tracking adjustment and the like for the objective lens. Further, in order to improve driving efficiency for the objective lens holder, some objective lens actuator are provided with a ferromagnetic yoke on the base member to draw effectively magnetic fluxes from the permanent magnets so that high density magnetic fluxes are given to the focus coil, the tracking coil and the tilting coil.
At this point, because vibration will occur in each of the metal wires due to driving of the objective lens holder, various artifices are employed to suppress the vibration. As one artifice, as shown in FIG. 12, a resin molded gel holder 102 having through holes 101 is fixed on the base member (not shown). Six metal wires 100 to hold the objective lens holder in a shakable manner with connection to the focus coil, the tracking coil, the tilting coil and the base plate (all not shown), are inserted through the through hole 101. A gel material containing silicon as a main ingredient, is filled in the through hole 101 in the gel holder 102. At this point, the gel material utilized here is hardened to gel by ultraviolet irradiation for a predetermined duration after the gel material is injected into each of the through holes 101 in the gel holder 102. By this arrangement, the vibration which is generated on each of the metal wires 100 can be attenuated and suppressed by the gel material in each of the through holes 101 in the gel holder 102.
However, as shown in FIG. 12, at the gel holder 102 in the conventional technology, the gel material must be injected from an opening of the through hole 101, in other words, from an insertion direction of the metal wires 100. Because the injection of the gel material is performed near the metal wires 100, a needle 103 of a gel dispenser may contact to the metal wires 100 during the injecting process for the metal wires 100 to be deformed especially when a number of the metal wires 100 inserted to the through hole 101 is large. In such a case, the tilting characteristics of the objective lens actuator becomes worse. Further, when viscosity of the gel material which is injected is high and speed of injecting is high, the gel material overflows from the opening of the through hole 101 before the gel material arrives at bottom of the through hole 101 because of the surface tension.
By this reason various technology is proposed to prevent problems which occur during the above described gel material injecting process. For example, JP-A-H11-265516 and JP-A-2005-116062 disclose the optical pickup device in that the through hole made in the gel holder into which the metal wires are inserted, has opening made in a side surface of the gel holder. By this arrangement, because the injecting process of the gel material is performed from the side surface of the gel holder, and contact of the needle of the gel dispenser to the metal wires are made less, efficiency of the gel material injecting process can be improved.
The optical pickup devices disclosed in JP-A-H11-265516 and JP-A-2005-116062, has merit that the gel material is easily filled because the through hole has the opening in the side surface through which the gel material is injected, however, on the other hand, the filled gel material tends to be formed in concave or convex shape at its surface of the opening in the vertical direction, and it is difficult to fill a given amount of the gel material into each of the through holes because the through hole is wide opened in the side surface. When the amount of the filled gel material at each through holes becomes different, control action against vibration for each of the metal wires which is inserted into each of the through holes is not performed evenly. This results in problems of deterioration of moving characteristics of the object lens and read and write characteristics of the optical pickup device.
For this problem, in JP-A-H10-106000, JP-A-2003-233919 and JP-A-2005-251295, an optical pickup device is disclosed in which an injection hole to fill the gel material is arranged on a side surface of the through hole formed in the gel holder. By this arrangement, when the gel material is filled from the injection hole, the gel material is not formed in concave or convex shape at its surface in the vertical direction, and the gel material can be filled equally in amount for each of the through holes.
In the structure of the optical pickup devices disclosed in JP-A-H10-106000, JP-A-2003-233919 and JP-A-2005-251295, the amount of the gel material filled in each of the through holes can become equal by the injection of the gel material through the injection hole arranged in the gel holder, however, it causes a problem that a tip portion of the needle tends to be inserted from the injection hole into inside of the through hole, and the needle may contact to the metal wires which are inserted into the through hole and then, may make the metal wires deformed if inner diameter of the injection hole is made larger than outer diameter of the needle. On the other hand, if the inner diameter of the injection hole is made smaller than the outer diameter of the needle, the tip portion of the needle tends to detach from the injection hole during the gel material injecting process because the tip portion of the needle is not located to fix to the injection hole, it causes a problem that the gel material adheres to surroundings of the gel injection hole. Further, if a shape of cross section of the tip portion of the needle and that of the injection hole are different, a space is formed between the needle and the injection hole when the tip portion of the needle is located at the injection hole, it causes a problem that the gel material spills out from the space during the gel injecting process.